1. Field of the Invention
The present invention generally relates to an inkjet head and a manufacturing method thereof and, more particularly, to an electrostatic inkjet head having an individual electrode structure in which a vibration plate is driven by an electrostatic force generated by the individual electrode, and also relates to a method of manufacturing such an inkjet head.
2. Description of the Related Art
Japanese Laid-Open patent application No. 6-71882 discloses an electrostatic inkjet head used for an on-demand inkjet printer. The inkjet head disclosed in this patent application has a vibration plate and an individual electrode located opposite to the vibration plate. The individual electrode is formed by an n-type or p-type diffusion layer formed in a single crystal silicon (Si) substrate. The individual electrode is isolated from the Si substrate by a p-n junction. In such an inkjet head structure, the vibration plate is deformed by supplying a voltage to the individual electrode so as to discharge droplets of ink from a nozzle connected to a space defined by the vibration plate.
In the above-mentioned electrostatic inkjet head, the individual electrode is isolated from the Si substrate via the p-n junction. Accordingly, a leak current flowing through the p-n junction area varies due to a deviation in a process of forming the p-n junction. Thus, a problem such as an increased power consumption, an unstable operation of the inkjet head or an insufficient drive power generated by a drive circuit may be caused by the p-n junction leakage or generation of a p-n junction capacitance.
Additionally, in the above-mentioned inkjet head, the individual electrode comprises a diffusion layer formed by doping n-type or p-type impurities into the Si substrate, and a drive voltage is provided to the individual electrode. Accordingly, the drive voltage is limited by a width of a depletion layer, and, thereby, the drive voltage must be a relatively low voltage. Usually, the drive voltage has a sufficient margin relative to a junction destruction voltage. However, in the above-mentioned inkjet head, since a relatively low voltage must be provided to the individual electrode, there is a problem in that a margin in the drive voltage provided to the individual electrode is small.
Further, the above-mentioned patent application describes an example of the inkjet head in which an individual electrode is provided in a groove formed in a glass substrate, which groove defines a gap between the individual electrode and the vibration plate. Since the groove is formed via a dry or wet etching method, the gap between the individual electrode and the vibration plate cannot be precisely controlled. Accordingly, when a plurality of grooves are formed on a wafer substrate, a uniform gap cannot be reliably achieved. The gap is an important design parameter which determines a drive characteristic of the inkjet head. Thus, if the gap is not uniform, a uniform characteristic of the inkjet head cannot be achieved.
To overcome the problems described above, the preferred embodiments of the present invention provide an improved inkjet head and a manufacturing method thereof wherein the inkjet head achieves a large margin in a drive voltage and prevents deviation in a drive characteristic of the inkjet head.
According to one preferred embodiment of the present invention, an electrostatic inkjet head has at least one ink chamber connected to an inkjet nozzle and is formed of a silicon substrate, the electrostatic Inkjet nozzle includes a vibration plate defining a part of the ink chamber, the vibration plate being elastically deformable so as to eject a droplet of ink from the inkjet nozzle, an individual electrode located opposite to the vibration plate with a predetermined gap therebetween, the individual electrode including a single crystal silicon substrate, and gap spacers disposed on the single crystal silicon substrate, the gap spacers being made of an insulating film so as to define the gap between the individual electrode and the vibration plate, wherein the individual electrode is made of a silicon film containing impurity atoms providing one of an n-type conductivity and a p-type conductivity to the individual electrode, and the individual electrode is surrounded by the gap spacers.
According to the above-mentioned preferred embodiment of the present invention, the individual electrode is surrounded by the gap spacers which are made of insulating films. Thus, the individual electrode is electrically insulated from other parts of the inkjet head such as the single crystal silicon substrate or other individual electrodes. As a result, a leak current from the individual electrode is significantly reduced which results in a low-power consumption inkjet head. Additionally, a margin of voltage between the individual electrodes is increased, which results in an increase in freedom of a driving voltage used to drive the inkjet head. Further, since the individual electrode is formed of the silicon film containing impurity atoms which provide an n-type conductivity or a p-type conductivity to the individual electrode, a resistance of the individual electrode is reduced, which results in a high-speed operation of the inkjet head.
In the electrostatic inkjet head according to preferred embodiments of the present invention, the silicon film forming the individual electrode may contain impurity atoms at a concentration of more than about 1E18/cm3. Accordingly, an ohmic contact can be easily obtained which increases reliability. Additionally, since a resistance of the individual electrode is reduced, a high-speed operation can be achieved.
The impurity atoms contained in the silicon film forming the individual electrode may be phosphorus atoms or arsenic atoms. Additionally, the impurity atoms contained in the silicon film forming the individual electrode may be boron atoms. This enables use of a manufacturing line of a conventional LSI semiconductor device, which results in reduction in a manufacturing cost of the inkjet head.
Additionally, there is provided according to another preferred embodiment of the present invention, an electrostatic inkjet head having at least one ink chamber connected to an inkjet nozzle, the electrostatic inkjet head including a silicon substrate, the electrostatic inkjet nozzle including a vibration plate defining a part of the ink chamber, the vibration plate being elastically deformable by an electrostatic force so as to eject a droplet of ink from the inkjet nozzle, an individual electrode located opposite to the vibration plate with a predetermined gap therebetween, the individual electrode being made of a single crystal silicon substrate, and gap spacers formed on the single crystal silicon substrate, the gap spacers including an insulating film arranged to define the gap between the individual electrode and the vibration plate, wherein the individual electrode includes a silicon film and a silicide film formed on the silicon film, the silicon film lacking impurity atoms providing one of an n-type conductivity and a p-type conductivity to the individual electrode, and the individual electrode is surrounded by the gap spacers.
According to the preferred embodiment described in the preceding paragraph, the individual electrode is surrounded by the gap spacers which are made of insulating films. Thus, the individual electrode is electrically insulated from other parts of the inkjet head such as the single crystal silicon substrate or other individual electrodes. Thus, a leak current from the individual electrode can be reduced which results in a low-power consumption inkjet head. Additionally, a margin of voltage tolerance between the individual electrodes is increased, which results in an increase in freedom of a driving voltage for driving the inkjet head. Further, since the individual electrode is made of the silicon film and the silicide film formed on the silicon film, a resistance of the individual electrode can be reduced without introducing impurity atoms into the silicon film, which results in a high-speed operation of the inkjet head.
Additionally, in the electrostatic inkjet head according to preferred embodiments of the present invention, the individual electrode may include a silicide film formed on the silicon film containing the impurity atoms. Accordingly, a resistance of the individual electrode can be greatly reduced, which results in a high-speed operation of the inkjet head.
In the electrostatic inkjet head according to preferred embodiments of the present invention, the silicide film may be made of titanium silicide. Since the titanium silicide has excellent heat resistance, there is less limitation in the subsequent heat treatment and a freedom in process design is increased. Additionally, this enables use of a process line of a conventional LSI semiconductor device, which results in reduction in a manufacturing cost of the inkjet head.
The electrostatic inkjet head according to preferred embodiments of the present invention may further include an insulating film formed on the silicon film of the individual electrode. The insulating film prevents the vibration plate from contacting the individual electrode during operation. Thus, a malfunction due to short-circuiting between the vibration plate and the individual electrode can be prevented.
Additionally, in the electrostatic inkjet head according to preferred embodiments of the present invention, the insulating film may be made of silicon nitride. Since the silicon nitride has excellent insulation characteristics, a malfunction due to short-circuiting between the vibration plate and the individual electrode can be reliably prevented. Additionally, use of the silicon nitride enables allows a manufacturing line of a conventional LSI semiconductor device to be used, which results in reduction in a manufacturing cost of the inkjet head. Further, since the silicon nitride film used as a mask for forming the individual electrode can be used as an insulating film on the individual electrode, a number of process steps required for manufacturing the inkjet head is reduced.
Alternatively, the insulating film may be made of silicon oxide. Since the silicon oxide has excellent insulation characteristics, a malfunction due to short-circuiting between the vibration plate and the individual electrode can be reliably prevented. Additionally, use of the silicon oxide enables use of a process line of a conventional LSI semiconductor device, which results in reduction in a manufacturing cost of the inkjet head.
Additionally, according to another preferred embodiment of the present invention, methods for manufacturing the above-mentioned electrostatic inkjet heads are provided.
Other objects, features and advantages of the present invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings.